In order to remove substances usually eliminated with urine and for fluid withdrawal, various methods for extracorporeal blood treatment or cleaning are used in chronic kidney failure. In hemodialysis, the patient's blood is cleaned outside the body in a dialyzer. The dialyzer comprises a blood chamber and a dialyzing fluid chamber, which are separated by a semipermeable membrane. During the treatment, the patient's blood flows through the blood chamber. In order to clean the blood effectively from substances usually eliminated with urine, fresh dialyzing fluid flows continuously through the dialyzing fluid chamber.
Whereas the transport of the low-molecular substances through the membrane is essentially determined by the concentration differences (diffusion) between the dialyzing fluid and the blood in hemodialysis (HD), substances dissolved in the plasma water, in particular higher-molecular substances, are effectively removed in hemofiltration (HF) by a high fluid flow (convection) through the membrane of the dialyzer. In hemofiltration, the dialyzer functions as a filter. Hemodiafiltration (HDF) is a combination of the two processes.
In hemo(dia)filtration, part of the serum drawn off through the membrane is replaced by a sterile substitution fluid, which is fed to the extracorporeal blood circuit either upstream of the dialyzer or downstream of the dialyzer. The supply of substitution fluid upstream of the dialyzer is also referred to as pre-dilution and the supply downstream of the dialyzer as post-dilution.
In the known hemo(dia)filtration apparatuses, the substitution fluid is fed to the extracorporeal blood circuit from the fluid system of the machine via a substitution fluid line. With pre-dilution, the substitution fluid line leads to a connection point on the arterial blood line upstream of the dialyzer or filter, whereas with post-dilution the substitution fluid line leads to a connection point on the venous blood line downstream of the dialyzer. The substitution fluid line generally has a connector, with which it can be connected either to the venous or arterial blood line. In order to interrupt the fluid supply, a clamp or suchlike is provided on the substitution fluid line. A hemo(dia)filtration apparatus of this kind is known for example from European Patent Application Publication No. EP-A-0 189 561.
The monitoring of the blood treatment requires a knowledge of whether the substitution fluid is fed to the extracorporeal blood circuit upstream or downstream of the dialyzer or filter. European Patent Application Publication No. EP-A-1 348 458 describes a method and a device for monitoring the supply of substitution fluid for an extracorporeal blood treatment apparatus. The propagation time of the pressure waves of a substituate pump disposed in the substitution fluid line is measured for the detection of the supply of substitution fluid upstream or downstream of the dialyzer or filter. The supply of substitution fluid upstream or downstream of the dialyzer or filter is detected on the basis of the propagation-time measurement. The known method requires the use of a substituate pump generating pressure waves.
The blood treatment apparatus known from European Patent Application Publication No. EP-A-1 595 560 makes provision, for the detection of a pre- or post-dilution, to measure the pressure in the blood circuit downstream of the dialyzer or filter, whereby a pre- or post-dilution is detected on the basis of the change in the pressure after the switching-off and/or switching-on of the substituate pump provided for the delivery of the substitution fluid.
In practice, the pre- or post-dilution is preselected by the user by the fact that the substitution fluid line is connected either upstream of the dialyzer or filter to the arterial blood line or downstream of the dialyzer or filter to the venous blood line. Furthermore, the user preselects the treatment parameters required for the given blood treatment. There is a risk here that, after insertion of the hose system intended for one-off use, which comprises the arterial and venous blood line as well as the substitution supply line, the substitution supply line for a blood treatment with a pre-dilution is connected not to the arterial admission point, but rather to the venous admission point. Conversely, there is the risk that, for a post-dilution, the substitution line is connected not to the venous admission point, but rather to the arterial admission point. If the incorrect connection of the substitution line is not noticed, it can lead to considerable complications. In the case of a post-dilution with excessively high substitution flows, for example, it can lead to a high hemoconcentration and coagulation in the dialyzer or filter.